Such an engine type, as better described in French patent applications No. 2,818,324 and 2,818,325 filed by the applicant, comprises at least a cylinder, a piston sliding in this cylinder, a combustion chamber delimited on one side by the upper face of the piston comprising a teat arranged in the centre of a concave bowl and at least one injection nozzle for injecting fuel with a nappe angle less than or equal to
      2    ⁢    Arctg    ⁢          CD              2        ⁢        F              ,where CD is the diameter of the cylinder and F the distance between the point of origin of the fuel jets from the injection nozzle and the position of the piston corresponding to a crank angle of 50° to the top dead centre.
Thus, in case of early injection, i.e. when the position of the piston is in the vicinity of 50° crank angle for the injection phase selected in relation to the piston top dead centre, the fuel does not come into contact with the cylinder wall and it mixes with the air or the mixture of air and of recirculated exhaust gas present in the combustion chamber.
In this type of engine, the applicant has used a bowl with particular values for the vertex angle of the teat (0° to 30° greater than those of the nappe angle) that allow to obtain homogeneous mixing of the fuel mixture upon injection.
The applicant has continued its research on this vertex angle and has obtained results according to which this vertex angle can be increased even further while improving the engine performances, as regards power as well as emissions such as soot emissions.